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The mixture of gibberellins A and A GA can increase flowering in conifers if applied at the correct time, duration and concentration Cecich, 1983; Marquard and Hanover, 1984; Pollard an

Gibberellin A enhances flowering

of Picea glauca grafts in two consecutive years

1 USDA-Forest Service, Columbia, MO 65211, and

2

USDA-Forest Sf-rvice, Rhinelander, WI 54501 U.S.A

Introduction

Trees that flower abundantly in one year

and then bear sparsely or not at all for

several years are said to show periodicity

of flowering This infrequent, unpredictable

flowering behavior has led to inefficient

seed collecting and seed orchard

opera-tions Therefore, treatments to alleviate

such flowering problems in conifers have

been the subject of much recent

experi-mentation

The mixture of gibberellins A and A

(GA

) can increase flowering in conifers

if applied at the correct time, duration and

concentration (Cecich, 1983; Marquard

and Hanover, 1984; Pollard and Portlock,

1983) Except for Marquard and Hanover

(1985), all experiments with GA have

been done on plants never previously

treated There have been no reports of

GA

being applied to the same tree or

seedling, or even the same branches, in

two consecutive years Our paper reports

the results of an experiment on Picea

glauca (Moench (Voss)) grafts in which

GA was applied to the same branches

in two consecutive years in an attempt to

overcome periodic flowering.

Materials and Methods

Readers are referred to Cecich (1985) for details of the experimental design and treat-ment procedures The first GA applications

were made in 1982 In 1983, GAwas again sprayed on the same trees and branches on the

same dates Length of the terminal shoot on all

the treated and control lateral branches was

measured in August 1983 and 1984 Ovulate and staminate strobili were counted in early May 1983 and 1984 Flowering data were

trans-formed to log,, (x + 1) and evaluated by a

com-bined analysis of variance and Duncan’s new multiple range test Simple correlation coeffi-cients were computed for the 1983 and 1984

flowering and branch length data.

Results

The 1983 flowering results for the 5

early-flushing (EF) and 5 late-flushing (LF) white spruce clones have been published

else-where (Cecich 1985), but treatment

means are summarized in Table I for convenience of comparison with the 1984

mean results In both years, the GA

treated branches on ramets of the EF and

LF clones produced significantly more

ovulate and staminate strobili than

paired

1984, the LF clones again produced

signi-ficantly more ovulate strobili than the EF

clones This was reversed for staminate

strobili; that is, the EF clones produced

more than the LF clones

Spraying with GA in 1982 had no

effect on lateral branch length of either the

EF or LF clones in 1983 However, in

1984 the GA -treated branches were

about 25% shorter than the control

branches The EF clones had a mean

length of 185 mm for the controls and

141 mm for the GA atca branches

The LF control !a!nets had an average

branch length of 217 mm, while the

treat-ed branches were 163 mm long.

Treated branches on EF and LF clones

responded with significant increases in

flowering in 1983 and 1984 (Table I).

Interactions were due to a change in

magnitude of response, rather than to a

change in rank of the treatment

combina-tions Clone x treatment interactions for

staminate strobilus production tP <- 0.01)

were apparently more complex than for

ovulate strobilus production (NS) in that

they were not related to flushing type but

to specific clones

Ovulate and staminate strobilus

produc-tions in 1983 and 1984 were significantly

correlated (r = 0.760 ) Branch length was

negatively correlated with production of

ovulate strobili (r = -0.758 ) and staminate

strobili (r = -0.931 **

This report is the first to describe the

suc-cessful stimulation of male and female

flowering in a conifer by consecutive

annual treatments with GA4!7 The 1984 results substantiated the 1983 observa-tions that the treated LF ramets produced significantly more ovulate strobili than the treated EF ramets In 1983, there was no

difference in s!laminate strobilus

produc-tion between EEF and LF clones but, in

1984, the EF clones produced significantly more staminate strobili than the LF clones

In unpublished experiments, flowering was

promoted by G in both flushing types; but the response was closely related to a common date (June 20), indicating a pos-sible environmental control, or a larger than expected ’window’ for treatment application Needles of the elongating

branch tips in the EF families began to

harden on June 13, 1 wk before the

opti-mum treatment date Needle

harden-ing was noted 1 wk later in the LF families

Hardening of the needles could potentially

be used to determine when to apply

GA

Branch length reduction by a heavy

flowering/cone crop could affect the use of

a certain percentage of the previous year’s growth as an index of when to apply

GA The final length of the treated branches in 1984 was 75% of the control

length and 70&dquo;/° of the previous year’s s

length

proposed index of 90% (Owens and

Mol-der, 1977) or 75% (Marquard and

Hano-ver, 1984) for GA application, the

’win-dow’ would have been missed Under

these circumstances, calendar dates,

needle hardening and/or bud morphology

may be preferred for scheduling

treat-ments

These results suggest that periodic

flow-ering in white spruce can be overcome

with judicious spray application of GA

Furthermore, the lack of significant

inter-actions for clone x treatment and clone x

year for ovulate strobili suggests that

GA can be used to overcome clonal

variation in female flowering However,

unequal representation of clones as pollen

parents, as exemplified by the strong

clone x treatment interaction, might be a

possible concern for an orchard manager

Conclusions

Although the present data are

encour-aging that year-to-year regularity in seed

production can be achieved, additional

experiments required number of years in which a significant

re-sponse can be elicited

References

Cecich R.A (1983) Flowering in a jack pine seedling seed orchard increased by spraying with gibberellin A 4/7 - Can J For Res 13,

1056-1062 Cecich R.A (1985) White spruce (Picea glau-ca) flowering in response to spray application of gibberellin A - Can J For Res 15, 170-174 Marquard R.D & Hanover J.W (1984) Relation-ship between gibberellin A concentration,

time of treatment, and crown position on flow-ering of Picea glauca Can J For Res 14,

547-553 Marquard R.D & Hanover J.W (1985) Floral

response of Picea glauca to gibberellin A 4/7’ naphthalene acetic acid, root pruning, and bien-nial treatment Can J For Res 15, 743-746 Owens J.N & Molder M (1977) Bud

develop-ment in Picea glauca 11 Cone differentiation and early development Can J Bot 55,

2746-2760

Pollard D.F.W & Portlock F.T (1983) Timing and duration effects of gibberellin and fertilizer

treatment on strobilus production in young

western hemlock Can For Serv Res Notes 3,

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